THEORIES OF PLATE TECTONICS
Alfred Lothar Wegener
Lived 1880-1930
German Meteorologist and Geophysist
Pangaea Theory – claimed that the continents had formed a single landmass, which split
apart. Wegener was not the first to suggest that the continents had been one, but was the first
to present evidence from several fields.
1912-Continental Drift Theory – Wegener noticed that there were similar glacial deposits in
South America and Africa. He also found that fossils often indicated a climate very different
from the climate of today , such as fossils of tropical plants found on an Arctic island, Fossil
remains of a specific reptile were found on continents that once touched. All of these facts
supported theory of continental drift. Wegener’s hypothesis lacked a geological mechanism to
explain how the continents could drift across the Earth’s surface.
Harry Hess
Lived 1906-1969
American Geologist
1962 –Sea Floor Spreading Theory – idea that the seafloor itself moves and carries continents
with it, as it expands from a central point,. The theory is well-accepted now. It is caused by
convection currents in the molten, very weak upper mantle, or asthenosphere.
Hess described a geologic mechanism to account for Wegener’s moving continents. He said it
was possible that molten magma from beneath the earth’s crust could ooze up between the
plates in the rift in the ocean floor. As the hot magma cooled in the ocean water, it would
expand and push the plates beside it. North and South America would move to the west and
Eurasia and Africa would move to the east. The Atlantic Ocean would get wider, but the
coastlines of the landmasses would not change dramatically.
Dan McKenzie
Lives 1942 –
English Geophysicist
1968 – Theory of Plate Tectonics- is a combination of two earlier ideas: continental drift and
sea-floor spreading. This theory was formed as new information was learned about the nature
of the ocean floor, Earth’s ancient magnetism patterns, the location of volcanoes and
earthquakes, the flow of heat from Earth’s interior, and the worldwide distribution of plant
and animal fossils.
Earth’s outermost layer, the lithosphere, is broken into 7 large, rigid pieces called plates; the
African, North American, South American, Eurasian, Australian, Antarctic and Pacific plates.
Several minor plates also exist, The plates are all moving in different direction and at different
speeds, from 2 cm to 10 cm per year in a relationship to each other.
The main features of plate tectonics are;
 The Earth’s surface is covered by a series of crustal plates.
 The ocean floors are continually moving, spreading from the center, sinking at the edges
and being regenerated.
 Convection currents beneath the plates move the crustal plates in different directions.
 The source of heat driving the convection currents is from radioactivity deep in the
Earth’s mantle.